In hydraulically actuated fuel injection systems, a control valve body is provided with a valve system having grooves or orifices which allow fluid communication between working ports, high pressure ports, and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid which is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current configurations, a driver will deliver a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift an armature into the open position so as to align grooves of the control valve body and the armature. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure plunger chamber. As the pressure in the high pressure plunger chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.
However, in such a conventional system, the armature has a tendency to bounce or repeatedly impact against the open coil during the opening stroke. During this bouncing, it is difficult to control the armature motion and hence results in the inability to efficiently control the supply of fuel to the combustion chamber of the engine. For example, in conventional systems it is not possible to quickly move the armature away from the open coil in order to minimize the bouncing effect during an injection of a pilot quantity of fuel. Accordingly, the initial quantity of fuel provided during the pre-stroke event cannot be easily controllable, resulting in a larger injection quantity of fuel than desired. This may result in a retarded start of injection, as well as the inability to control the armature and hence the injection of a small, pilot quantity of fuel. That is, during this bouncing or repeated impact, a small quantity of fuel cannot be metered accurately in order to efficiently inject this small quantity of fuel into the combustion chamber of an engine. Additionally, it is also very difficult, if not impossible, to vary the amount of fuel during this small injection.
Thus, injection shot-to-shot variations can occur on a single fuel injector.
It is also known that the bouncing phenomenon may differ from injector to injector, and over time. For example, different manufacturing tolerances may affect the bouncing phenomenon from, for example, small variations in armature diameter to different coil characteristics. Additionally, over time, in the same injector, variations may result from different operating conditions such as temperature and wear on the parts due to aging and other factors. Hence, the control of fuel quantity may vary from fuel injector to fuel injector, as well as over time with the same fuel injector. This also may lead to higher emissions and engine noise. Thus, injector shot-to-shot variations can occur on the same engine between multiple injectors.
The shot-to-shot variations mentioned above can cause idle stability issues that are detectable by the vehicle's operator and can cause decreased engine efficiency and increased emissions. Currently, manufacturing tolerances of the injector require sorting or rework to improve shot-to-shot variations.
Thus, there is a need to reduce injector shot-to-shot variations in an injection system by reducing the bounce of an armature of a control valve of the system.